Method of making an optoelectronic interface module

ABSTRACT

A flexible circuit film (103) having a plurality of electrical tracings (118) is provided. A mold (102) having a cavity (112) capable of accepting the flexible circuit film (103) is provided. The flexible circuit film (103) is placed into the mold (102). A first optical portion (203) is molded with the flexible circuit film (103) in the cavity (112) of the mold (102) so as to join the flexible circuit film (103) to the first optical portion (203).

BACKGROUND OF THE INVENTION

This invention relates, in general, to fabrication of optical devicesand, more particularly, to manufacturing an optoelectronic interfacesubmodule.

This application is related to issued U.S. Pats. bearing U.S. Pat. Nos.5,265,184 and 5,276,754, titled MOLDED WAVEGUIDE AND METHOD OF MAKINGSAME and OPTOELECTRONIC MOUNT AND METHOD FOR MAKING, filed on May 28,1992 and on Aug. 31, 1992, issued on Nov. 23, 1993 and Jan. 4, 1994which are hereby incorporated by reference herein. Further, thisapplication is related to application bearing Ser. No. 08/019,731,titled MOLDED WAVEGUIDE WITH A UNITARY CLADDING REGION AND METHOD OFMAKING, filed on Feb. 19, 1993.

At present, interconnection of a photonic device and a waveguide to forman optoelectronic interface submodule is a difficult task that typicallyemploys a manual method or a semi-automatic method for interconnectingor mating of the waveguide and the photonic device. Further,interconnection of the optoelectronic interface submodule to aninterconnect substrate also is achieved by either a manual method or asemi-automatic method such as wire bonding. These manual orsemi-automatic methods for interconnecting the optoelectronic interfacesubmodule to the interconnect substrate typically are difficult tasksthat are complex, inefficient, and not suitable for high volumemanufacturing.

For example, one major problem associated with interconnection of theoptoelectronic submodule to an interconnect substrate is devising afabrication method and a structure that allows electrical and mechanicalcoupling between the optoelectronic interface submodule and theinterconnection substrate. As practiced in the prior art,interconnection of the optoelectronic submodule to the interconnectsubstrate is achieved by carefully positioning the preparedoptoelectronic substrate on the interconnect board and subsequently wirebonding the photonic devices so as to achieve electrical interconnectionbetween the photonic devices and the interconnect board. However, manyproblems arise by wire bonding the optoelectronic submodule to theinterconnect board, such as being extremely labor intensive, costly,inaccurate, as well as providing additional problems with encapsulation,such as wire sweep, reliability, and the like, Moreover, if for anyreason one of the wire bonds is unsuitable or unreliable, product can bemanufactured that is both unreliable or unusable, thus increasing costand reducing manufacturing capability.

It can be readily seen that conventional methods for interconnecting anoptoelectronic interface submodule to an interconnect substrate havesevere limitations. Also, it is evident that conventional processes thatare used to fabricate interconnection between the interconnect substrateand the photonic devices are extremely fragile and are susceptible toboth reliability and manufacturing problems. Further, the conventionalmanufacturing methods are not only complex and expensive, but also arenot amenable to high volume manufacturing. Therefore, a method andarticle for interconnecting a prepared optoelectronic interfacesubmodule and an interconnect substrate is highly desirable.

SUMMARY OF THE INVENTION

Briefly stated, a method is provided that joins a flexible circuit filmto an optical portion. A flexible circuit film having a plurality ofelectrical tracings is provided. A mold having a cavity capable ofaccepting the flexible circuit film is provided. A flexible circuit filmis placed into the mold. A first optical portion is molded with theflexible circuit film in the cavity of the mold so as to join theflexible circuit film to the first optical portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a greatly enlarged simplified perspective view, portionsthereof removed and shown in section, of a mold;

FIG. 2 is a greatly enlarged simplified perspective view of a flexiblecircuit film joined to an optical portion; and

FIG. 3 is a greatly enlarged simplified perspective view of anoptoelectronic submodule mounted on an interconnect substrate.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a greatly simplified enlarged perspective view, portionsthereof removed and shown in section, of a mold 102 capable of acceptinga flexible circuit tape 103. It should be understood that FIG. 1 hasbeen greatly simplified, thus many specific engineering details havebeen omitted from the illustration, thereby more clearly illustratingthe present invention.

Generally, mold 102 is similar to the molds described in allapplications referenced hereinabove. Briefly, mold 102 includes a firstportion or upper portion 106 and a second portion or lower portion 107.

Upper portion or first portion 106 of mold 102 has a surface 108 thatcomes in contact with a surface 109 of flexible circuit film 103.Surface 108 of first portion 106 generally is a flat surface that iscapable of being modified to a variety of structures that facilitatemoving, holding, and positioning of flexible circuit film 103 inrelation with surface 108.

Lower portion or second portion 107 of mold 102 is made to provide acavity 112. It should be understood that cavity 112 forms a sealedchamber (not shown) when first portion 106 and second portion 107 arecompressed together with flexible circuit film 103 therebetween.Further, it should be realized that portions of mold 102 and a portionof flexible circuit film 103 have been removed to show internal featuresthereof. Generally, cavity 112 is capable of being shaped or formed intoany suitable shape or form. The shape or form of cavity 112 isapplication specific, thus allowing a large variety of features havingdifferent shapes and sizes to be formed. For example, indents or groovesare capable of being molded that upon subsequent processing will formcore regions, alignment guides are capable of being molded, and ofcourse, specific dimensions of cavity 112 vary depending upon thespecific application. Additionally, cavity 112 is capable of beingconfigured or made to accept core regions 117; however, it should beunderstood that core regions 117 are not necessary for the presentinvention. For example, cavity 112 could be used to mold an opticalportion or a first optical portion not having core regions, such as afirst cladding region which is subsequently adhered to a second claddingregion or second optical portion to form a waveguide core regions.Additionally, lower portion 107 of mold 102 includes an input port 113enabling injection, illustrated by arrow 114, of molding compounds intocavity 112.

Flexible circuit tape 103 is made from any thin insulative material,such as those typically suitable for Tape Automated Bonding (TAB)backing layer or substrate. As an example, polyimide is a representativematerial, but is certainly not the only one; polyimide type materialsare capable of being found under the tradename such as "UPLEX" or"KAPTON", among others. Other suitable materials include, but are notnecessarily limited to polyester material (lower in cost and performancethan polyimide), mylar materials, and composite materials, such as aresin filled epoxy or fiber reinforced materials.

Flexible circuit tape 103 bears a plurality of conductive tracings or aplurality of electrical tracings 118, more fully illustrated in FIG. 2,disposed either thereon or therein, that are formed by any suitablemethod, such as but not limited to plating, etching, photolithography,printing, etc. Typically, the plurality of conductive tracings or theplurality of electrical tracings 118 are made of a metal or metal alloy,such as copper, aluminum, tin, or titanium/tungsten (TiW), or the like.Adhesion of the plurality of conductive tracings 118 to the substrate119 is such that a plurality of conductive tracings 118 will notdelaminate or separate from substrate 119 when flexible circuit tape 103is bent or formed into position. The plurality of conductive tracing 118is capable of having a thickness 110 that ranges from 5.0 mills to 50.0mills. However, in a preferred embodiment of the present invention, anominal thickness 110 of the plurality of conductive tracings rangesfrom 15.0 mills to 20.0 mills.

Molding material or molding compound used for molding or injecting intocavity 112 of mold 102 is capable of being any suitable material, suchas polymers, epoxies, plastics, polyimides, or the like. In a preferredembodiment of the present invention, epoxy materials are used to fillcavity 112 so as to form a first optical portion 203, shown in FIG. 2,and bond flexible circuit film 103 to first optical portion 203. Ingeneral, molding parameters such as pressure, time, and temperature usedto mold or inject the molding material into cavity 112 of mold 102 rangeapproximately from 20.0 pounds per square inch to 2,000 pounds persquare inch, from 2.0 minutes to 20.0 minutes, and from 150.0 degreesCelsius to 300.0 degrees Celsius, respectively. Further, materialsselected for manufacturing of flexible circuit tape 103 are compatiblewith the molding parameters of the specific molding compounds ormaterials used. For example, in a preferred embodiment of the presentinvention, epoxy material is used for the molding compound and polyimidematerial is used for substrate 119 of flexible circuit tape 103.Additionally, it should be understood that materials selected forsubstrate 119 are capable of bonding or joining with molding materialsthat are injected into cavity 112 through port 113, thus upon completionof the molding process flexible circuit film 103 is joined or bonded tothe shape or form that is defined by cavity 112. Further, it should beevident that materials that exceed these requirements or performancelevels are also suitable to be used.

As can be seen in FIG. 1, flexible circuit tape 103 is provided withopenings 122. Openings 122 allow flexible circuit tape 103 to be movedor indexed in a continuous fashion, thus allowing the molding processthat joins flexible circuit tape 103 to the form molded in cavity 112 tobe automated. Moreover, openings 122 offer a further advantage ofaligning flexible circuit tape 103 to mold 102.

In the present invention, joining or mating of flexible circuit tape 103to the form or the shape that is molded in cavity 112 is achieved by wayof example with the following steps. With first portion 106 and secondportion 107 open to expose cavity 112, flexible circuit tape 103 isindexed to an appropriate position. Upon completion of indexing offlexible circuit tape 103, first and second portions 106 and 107 areclosed on flexible circuit tape 103, thus surface 108 of first portion106 is in contact with surface 109 of flexible circuit tape 103 and aportion 123 of surface 124 of flexible circuit tape 103 is in contactwith surfaces 126 of lower portion 107, thereby sealing cavity 112 alongit's periphery by the contact between surface 123 and surface 126. Itshould be evident that elements, such as core regions 117 that requireencapsulation by molding materials need to be placed into cavity 112prior to closing or sealing of upper portion 106 and lower portion 107.

Upon sealing or closure of upper portion 106 and lower portion 107 withflexible circuit tape 103 therebetween, molding material is injected into cavity 112, indicated by arrow 114, through input port 113, therebyfilling cavity 112. Additionally, it should be pointed out that specificoptical qualities of the molding material that is injected into cavity112 is dependent upon specific applications. For example, with coreregions 117 being placed inside cavity 112, final refractive index ofmolding material that is injected into cavity 112 typically is adjustedso that core regions 117 have at least a 0.01 higher optical refractiveindex, thus guiding light effectively and efficiently through coreregions 117. In yet another example, suitable molding material isinjected into cavity 112 to form a first optical portion that issubsequently processed, for example, joined with an optical adhesive toa second optical portion in order to form a waveguide having coreregions.

Referring now to FIG. 2, a partially completed optical interfacesubmodule 202 having an optical portion 203 that is joined or bonded toflexible circuit film 103. It should be understood that features orelements previously discussed in FIG. 1 will retain their originalidentification numerals. Further, it should be understood that opticalportion 203 is a result of the molding process previously described inFIG. 1.

As can be seen in FIG. 2, the plurality of electrical tracings 118 arenow capable of being more fully illustrated. However, it should beunderstood that the plurality of electrical tracings 118 are capable ofhaving a large variety of configurations, thus the specificconfiguration illustrated in FIG. 2 is only representative of one ofmany configurations possible.

The plurality of electrical tracings 118 illustrated in FIG. 2 includeselectrical traces 208, 209, 211, 212, 213, 214, 216, bonding pads 217,and contacts 204 and 207. Bonding pads 217 are used for mountingintegrated circuit 218 to the plurality of electrical tracings 118,thereby mechanically and electrically integrating or interconnectingintegrated circuit 118 with the plurality of electrical traces 118.

Contacts 204 are capable of having a variety of functions, such assignal input and output, power input and output, and the like. Thesevarious functions are integrated into the plurality of electricaltracings 118 via electrical traces 109. Additionally, in this particularexample, contacts 207 function as a ground and are interconnected bytraces 208. Contacts 207 and electrical traces 208 are further connectedby electrical trace 211 which is further connected to electrical trace212. Electrical traces 212, 213, 214 and 216 extend out on peripheralportions 219 and 221, respectively. Further, contacts 204, contacts 207,electrical tracings 208, and areas 223 are located on peripheral portion222 of flexible circuit film 103.

Generally, partially completed optoelectronic interface submodule 202 isconfigured with an optical portion 203 being joined to flexible circuitfilm 103. It should be understood that since portions of flexiblecircuit film 103 were not in contact with the molding compounds duringthe molding process, peripheral portions 219, 221 and 222 result fromnot having the molding compound come in contact with peripheral portions219, 221, and 222.

Areas 223 of flexible circuit film 103 are optically transparent,thereby allowing optical signals to pass through areas 223. Areas 223are made optically transparent by any suitable method, such as removingportions of flexible circuit film 103, photolithographically processing,laser ablating, selecting a material that is transparent to a wavelengthof light that is intended to be used, or the like.

Peripheral portions 219, 221, and 222 are now capable of being formedalong surfaces 224, 226, respectively, and along a surface not capableof being viewed in this figure. By forming peripheral portions 219, 221,and 222 against surfaces 224 and 226 and the surface that is not visiblein this particular view, enables electrical tracings 212, 213, 214, 216,contacts 204, areas 223, and contacts 207 to be bent into a compactconfiguration. Additionally this compact configuration allows electricalcontinuity around the corners of optical portion 203. More particularlyelectrical tracings 212, 213, 214, and 216 are now capable of being usedas leads that are illustrated in FIG. 3.

Generally, the forming of peripheral portions 219, 221, and 222 isachieved by mechanically bending peripheral portions 219, 221, and 222into place. Additionally, peripheral portions 219, 221, and 222 arecapable of being secured by any suitable adhesive, such as opticallyclear or transparent epoxies, polyimides, or the like. Further, itshould be understood that use of a transparent adhesive may not benecessary for adhering of peripheral portions 219 and 221, adhesion ofperipheral portion 222 to surface 226, in a preferred embodiment woulduse an optically clear adhesive.

FIG. 3 is a simplified partially exploded perspective view of anoptoelectronic submodule 302 mounted on an interconnect board 303. Inthe present invention, optoelectronic submodule 302, photonic device 307and standard electronic components, illustrated by IC 314, areelectrically coupled to an interconnect substrate 303. Additionally, itshould be evident that many more different types, such as capacitors,resistors, and the like are capable of being mounted on interconnectsubstrate 303.

Optoelectronic submodule 302 is capable of being interconnected orelectrically coupled with a photonic device 307. Photonic device 307 iscapable of being an individual optical transmitter, such as a laser or alight emitting diode (LED) (not shown), an optical receiver or photodetector, such as a photo diode (not shown) or a combination of bothphoto transmitters and photo detectors.

Alternatively, photonic device 307 is capable of being a phototransmitter, photo receiver, or a combination of both photo transmittersand photo receivers that are mounted on optoelectronic submodule 302.Photonic device 307 is mounted to optoelectronic submodule 302 in such amanner that individual working portions 305 of photonic devices 307 arealigned to core regions 227 through areas 223 of flexible circuit film103. As shown in FIG. 3, photonic device 307 is mounted tooptoelectronic submodule 302. Typically, photonic device 307 is mountedby any suitable method such as solder bump balls, electricallyconductive epoxy, or the like. More specifically, by way of examplesolder bump balls (not shown) serve to interconnect contacts 204 andcontacts 207 with a first and second contact (not shown) on photonicdevice 307, respectively. By accurately mounting photonic device 307 tooptoelectronic submodule 302, light transmission or light receptioninvolving a working portion 305 of photonic device 307 is directedthrough areas 223 of flexible circuit film 103 into or out of theplurality of core regions 227 (not shown in FIG. 3), thus maximizingsignal performance through optoelectronic submodule 203 while relaxingalignment tolerances of mounting photonic device 307 to optoelectronicsubmodule 302.

Generally, optoelectronic submodule 302 is mounted to interconnectsubstrate 303 by any suitable method. However, in a preferred embodimentof the present invention, terminal portions 228 of the plurality ofelectrical tracings 118 on peripheral portions 219 and 221 are trimmedand formed into "J" leads, thereby allowing easy and efficient surfacemounting of optoelectronic submodule 302 to interconnect substrate 303.For example, terminal portions 228 formed into "J" leads are surfacemounted to bonding pads 311 and 312. It should be evident that byforming terminal portions 228 into a surface mounting configuration suchas "J" leads enhances the ability to use automation for placing andmounting optoelectronic submodule 302 to interconnect substrate 303.Further, it should be pointed out that contacts 207, in this specificembodiment, are used for grounding structures; however, it should benoted that many other different types of grounding structures arecapable of being formed or utilized in the present invention.

Subsequent electrical coupling of standard electronic components, asillustrated by integrated circuit 314 on interconnect substrate 303 isachieved by ordinary methods well known in the art. It should be evidentby one of ordinary skill in the art, that many more electrical couplingstypically are necessary to fully utilize inputs and outputs of bothstandard electrical components and the optical components. It should befurther evident that standard input and output means, represented bylead 316, are used to couple other electronic components tointerconnection substrate 303. It should be also evident that while lead316 is shown in FIG. 3, other configurations of input and output meansor methods are capable, such as pin-grid arrays, bump bonding arrays, orthe like.

Further, plastic encapsulation of optoelectronic submodule 302 andinterconnect substrate 303 is capable of being achieved by anovermolding process, represented by plastic piece 317 which is capableof encapsulating interconnect board 303 and optoelectronic interfacesubmodule 302. However, it should also be understood that an alignmentguide, such as alignment ferrules are capable of being formed by severalmethods, such as molding, joining a first optical portion and a secondoptical portion to form an alignment guide, precision milling, and thelike so to enable engagement of alignment pins 318 (only one shown) withalignment ferrules, thereby providing accurate and repeatable alignmentof the plurality of core regions 227 (shown in FIG. 2) to an opticalcable 319 having an optical connector 321.

By now it should be appreciated that a novel method for joining aflexible circuit film to an optical portion and forming portions of theflexible circuit film into terminal ends such as "J" leads has beendescribed. The method and article of the present invention allow foreasy and efficient surface mounting of an optoelectronic interface to aninterconnect substrate, thereby incorporating and integrating photonicdevices with standard electronic components. Further the method andarticle of the present invention allow for integration of optoelectroniccomponents to standard electronic components in a cost effective mannerby providing a way to eliminate costly steps carried out by hand intoautomating these manufacturing steps.

What is claimed is:
 1. A method for joining a flexible circuit film toan optical portion comprising the steps of:providing a flexible circuitfilm having a plurality of electrical tracings; providing a mold havinga cavity capable of accepting the flexible circuit film; placing theflexible circuit film in the mold., the flexible circuit film having aportion of the plurality of electrical tracings extending beyond thecavity of the mold, thereby having the portion of the plurality of theelectrical tracings of the flexible circuit film that extends beyond afirst optical portion exposed; molding the first optical portion withthe flexible circuit film in the cavity of the mold so as to join theflexible circuit film to the first optical portion; providing a secondoptical portion; joining the first optical portion and the secondoptical portion with an optical adhesive to form a waveguide having acore region and a cladding region; and forming the portion of theplurality of electrical tracings that extends beyond the first opticalportion to a terminal end.
 2. A method for joining a flexible circuitfilm to an optical portion as claimed in claim 1 wherein the terminalend is shaped into a "J" lead configuration.
 3. A method for joining aflexible circuit film to an optical portion as claimed in claim 1wherein the step of joining the first optical portion and the secondoptical portion forms an alignment guide.